Power driven continuous cutting strip



J. W. EHLEN POWER DRIVEN CONTINUOUS CUTTING STRIP Sept. 23, 1969 2Sheets-Sheet 1 Filed D90. 28, 1966 INVENTOR JACK W. EHLEN ATTORNEYSSept. 23, 1969 w, EHLEN POWER DRIVEN cou'rmuous CUTTING STRIP 2Sheets-Sheet 2 Filed Dec. 28, 1966 FIG] ATTORNEYS United States PatentOffice 3,468,351 Patented Sept. 23, 1969 3,468,351 POWER DRIVENCONTINUOUS CUTTING STRIP Jack W. Ehlen, Torrance, Calif., assignor toMcCnlloch Corporation, Los Angeles, Calif., a corporation of WisconsinFiled Dec. 28, 1966, Ser. No. 605,371 Int. Cl. B27b 5/14, 17/08, 33/08U.S. Cl. 143-44 8 Claims ABSTRACT OF THE DISCLOSURE CROSS-REFERENCE TORELATED APPLICATION While this application involves several novelconcepts, it is related in part to the subject matter of United StatesPatent 3,338,275 filed Sept. 27, 1965.

BACKGROUND OF THE INVENTION The previously mentioned United StatesPatent 3,338,- 275 discloses a portable power saw comprising acontinuous cutting strip which is driven by a driving wheel about theperiphery of an elongated support member having a curved end. Thedriving member is driven by the power motor and is disposed inside theperiphery of the continuous cutting strip to drivingly contact portionsof the cutting strip.

A power saw constructed in accordance with United States Patent3,338,275 has been found to provide substantial advantages over aconventional chain saw. For instance, the relatively flexible,continuous cutting strips may be very economically manufactured, as bystamping, and may thus be thrown away when dull rather thannecessitating removal and sharpening. Because of the low inertiaresulting from the light weight of the continuous cutting strip, such aportable power saw may be virtually instantaneously stopped, thusallowing for ease of operation and reducing the hammering often createdby conventional chain saws. Further, the continuous cutting strip doesnot tend to carry a substantial amount of foreign material between thecutting teeth during a cutting operation, and the strip does not thensignificantly stretch. Because of its continuous smooth base surface,the continuous strip is easily installable or repaired, and provides asmooth outward flow of chips during a cutting operation.

While a power saw constructed in accordance with the previouslymentioned United States Patent 3,338,275 provides excellent cuttingcharacteristics in many respects, it has been found that the continuouscutting strip of such saws is sometimes subjected to wear due to theflexing imposed upon the strip by the elongated curved support member.

Additionally, since in such saws the driving member is disposed insidethe periphery of the continuous cutting strip, it has been found thatthe continuous strip sometimes tends to move away from the drivingmember upon the occurrence of substantial cutting forces. The drivingmember also sometimes tends to bend or kink the continuous cutting stripif the strip becomes bound or locked into the material being cut.

OBJECTS OF INVENTION Accordingly, a general object of the presentinvention is the provision of a method and apparatus for cutting whichminimizes or substantially eliminates disadvantages heretofore presentin power saw cutting.

A more specific object is the provision of a portable power saw whereinflexing of the cutting member is substantially eliminated.

A further object of the present invention is the provision of a cuttingdevice wherein the drive maintains driving contact with the cuttingmember even during the application of substantial cutting stresses.

Yet a further object of the present invention is the provision of animproved cutting device having a very lightweight and economical, yetefficient, continuous cutting member.

It is a still further object of the present invention to provide acutting device which does not tend to retain or carry substantialamounts of foreign material between the cutting teeth during cutting toreduce stretching of the cutting device.

Another object of the present invention is to provide a continuouscutting device having an interrupted surface to provide a smooth outwardflow of chips during a cutting operation.

Yet another object of the present invention is to provide an easilyinstallable cutting member which does not tend to kink.

It is a further object of the invention to provide a cutting memberwherein the individual cutting elements are integral with the cuttingmember in order to eliminate rear-back and to substantially eliminatetwisting of portions of the cutting member.

It is a still further object of the present invention to provide acutting device which may be virtually instantaneously stopped because ofrelatively low inertia.

Another object of the present invention is to provide a cutting devicewhich due to low frictional losses does not generate a substantialamount of heat.

A still further object of the present invention is the provision of acutting device wherein the tension of the rotating cutting member may beselectively adjusted.

SUMMARY OF THE INVENTION In achieving these and other objects which willbe apparent hereinafter, one aspect or the present invention provides asupport defining a substantially circular and continuous travel path,with a radially flexible continuous cutting strip rotatably disposed inthe travel path. The cutting strip may include a plurality of integralcutting teeth bent transversely. Driving means rotates the cutting stripthrough the substantially circular travel path.

Another aspect of the present invention provides a flexible cuttingstrip having a generally flat base portion with a plurality oftransversely spaced cutting teeth pairs intergrally inclined from thebase portion.

Another important aspect of the present invention comprises a method ofcutting wherein a radially flexible continuous cutting strip issupported and driven about a continuous circular travel path to preventflexing of the cutting strip.

THE DRAWINGS The invention and its many advantages may be furtherunderstood by reference to the following detailed descriptionillustrated in the accompanying drawings, in which:

FIGURE 1 is a side view of a portable power saw constructed inaccordance with the present invention;

FIGURE 2 is a side view of a preferred embodiment of a portion of thecutting strip of the present invention;

FIGURE 3 is a top view of a preferred embodiment of another portion ofthe cutting strip of the present inven tion;

FIGURE 4 is a detailed side view of the cutting strip driving portion ofthe present invention;

FIGURE 5 is a cross-sectional view of the driving mechanism taken alongthe line 5-5 of FIGURE 4;

FIGURE 6 is a cross-sectional view of the support adjustment taken alonglines 66 of FIGURE 4; and

FIGURE 7 is a cross-sectional view of a portion of the lubricationsystem of the present invention taken along lines 7-7 of FIGURE 4.

DETAILED DESCRIPTION OF THE INVENTION Referring to FIG. 1, a portablesaw constructed in accordance with the present invention is powered by aconventional gasoline motor designated generally at 10 and having a pairof handles 12 and 14. The gasoline motor 10 may be conventionallystarted by manual operation of the starter 16.

Rigidly connected to a support extension 18 is a hollow circular supportmember 20 which defines a substantially circular and continuous travelpath for a continuous cutting strip 22. The cutting strip 22 isconstructed from relatively thin metal to be radially flexible and isthus incapable of withstanding the forces of cutting without the supportmember 20. The support member 20 may be made from 7075 ST heat treatedaluminum about .141 inch thick. In the preferred embodiment, an outerdiameter of about 11.46 inches for the support member 20 has beenadvantageously untilized. The cutting strip 22 is driven about thesupport member 20 by a drive sprocket wheel 24 which is disposed outsidethe periphery of the strip 22 and is rotated by a suitable drive belt26. The gasoline engine 10 powers a driving shaft 28 which in turnrotates the drive sprocket wheel 24 through drive belt or chain 26.

A shield member 30 is provided to protect the saw operator from therotating drive sprocket wheel 24. Guard members 32 and 34 are rigidlyconnected to the support member 20 by suitable fastening screws 35 inorder to shield the cutting edges of the rotating cutting strip 22. Anadusting screw 36 is disposed through an elongated slot 38 to connectone end of the circular support member 20 to the extension 18. Byadustment of the position of screw 36 in slot 38, the magnitude of thegenerally circular travel path provided by the outer periphery of thesupport member 20 may be varied to allow selective adustment of thetension of the rotating continuous cutting strip 22. The support member20 is provided with an expandable joint 40, to be later described inmore detail, to allow such adustment while maintaining a continuoustravel path. An outwardly extending bumper 42 may be suitably connectedto the support member 20 to provide a stop or pivot point about whichthe cutting device may travel during a cutting operation.

The continuous cutting strip 22 includes a plurality of integral cuttingteeth 44 for performing efiicient cutting operations, as will be latermore fully described. Additionally, the cutting strip 22 includes aplurality of spaced apart integral guide members 46 for encompassing aportion of the outer periphery of the circular support member 20 inorder to constrain the cutting strip 22 to follow the substantiallycircular travel path and prevent flexing of the strip. It has been foundthat significantly longer wear and lower frictional losses are providedby this aspect of the present invention.

FIGURE 2 discloses in detail a portion of a preferred embodiment of thepresent cutting strip 22. Each of the cutting teeth 44 have identicalcross-sectional configurations and are integrally connected with arelatively fiat base portion 48. The cutting teeth 44 are benttransversely of the base portion 48 at predetermined inclinations. Eachcutting tooth 44 includes a sharpened cutting surface 50 which may beslightly backwardly inclined in a trailing manner. It will beunderstood, however, that the cutting surface 50 could be positionedeither at a right angle with the base portion 48, in a forwardlyinclined leading position, or in combinations of all three positions. Aswill be later described in greater detail, a driving surface 52 is alsoprovided for each of the cutting teeth 44 to enable the flexible cuttingstrip 22 to be driven by the rotating drive sprocket 24.

The guide members 46 integrally connected to the fiat base 48 areconstructed with an identical cross-sectional configuration as thecutting teeth 44. This identical construction of both the cutting teethand guide members enables the present device to be easily manufactured,as by stamping from a single piece of metal. The guide members 46 aretransversely disposed in pairs along the fiat base 48, with each pairbeing bent radially inwardly from the base 48 to define a spaceencompassing a portion of the outer periphery of the support member 20to constrain the cutting strip 22 to follow a substantially circulartravel path.

FIGURE 3 shows a top view of a preferred embodiment of incliningconfigurations for the cutting teeth of the present cutting strip 22.The cutting teeth comprise a plurality of pairs of transversely spacedcutting teeth integrally connected to the fiat base portion 48. In orderto provide superior cutting characteristics, the cutting teeth pairs maybe longitudinally grouped along and bent relative to the base portion 48in recurring series of four different inclining configurations.

A first inclining configuration is illustrated by the cutting teeth pair54 and 56, wherein both of these cutting teeth are evenly substantiallyvertically inclined to the base portion 48. In practice, it has beenfound that a base portion 48 having a width of about .232 inch incombination with an outward spacing of about .168 inch from the top ofthe cutting tooth 54 to the top of cutting tooth 56 provides excellentcutting characteristics.

A second inclining configuration is illustrated by the positions of thecutting teeth pair 58 and 60, wherein each of the cutting teeth areevenly transversely inclined to the base portion 48 by a greater amountthan the first inclining configuration of cutting teeth 54 and 56. Inpractice, a spacing of about .336 inch from the top of cutting tooth 58to the top of cutting tooth 60 has been advantageously utilized.

In the third inclining configuration illustrated by the position ofcutting teeth 62 and 64, the cutting tooth 64 is inclined more so on afirst side of the base portion 48 than the cutting tooth 62 of the teethpair. In practice, the cutting tooth 64 is bent to a position slightlypast the center line of the fiat base 48, while the cutting tooth 62 isinclined only slightly more outwardly than the cutting tooth 54.

The fourth inclining cutting teeth configuration of the presentinvention is illustrated by the positions of cutting teeth 66 and 68.The cutting tooth 66 is inclined more soon a second side of the baseportion 48 than cutting tooth 68. The configuration of cutting teeth 66and 68 is opposite the configuration of cutting teeth 62 and 64, withthe top of cutting tooth 66 being bent just slightly past the center ofthe flat base portion 48. The inclination of cutting tooth 68 to theflat base 48 is only slightly more outwardly inclined than the cuttingtooth 56 previously described.

The continuous cutting strip 22 may be constructed from a single pieceof low carbon, SAE 1030-1050 steel that has been Austempered and cyanidehardened. Carbon may be added to the surface of the strip so thatAustempering will yield an improved hardened cutting edge.Alternatively, the top of the stamped out cutting strip may be coppermasked before cyanide hardening in order to provide harder surfaces onthe inside of the guide members and on the outside of the cutting teeth.

The ends of the present cutting strip 22 may be easily joined duringmanufacture or repaired upon breaking. For instance, a Thermite processmay be used to join the ends of the strip. Alternatively, the ends ofthe strip may be secured together by electric fusion welding, by buttWelding, or by brazing with a short overlap.

Although recurring series of four different inclining configurations areillustrated. it will be understood that recurring series of more or lessthan four inclining con figurations may also be advantageously utilized.Further, a cutting strip constructed in accordance with the previouslydiscussed United States Patent 3,338,275 may be utilized with thepresent saw. With the provision of the present cutting teeth incliningconfigurations, it has been found that the continuous cutting strip 22is less likely to bind in the material being cut. Further, a cuttingstrip constructed in accordance with this invention does not tend toretain or to carry substantial amounts of foreign material betweenadjacent cutting teeth during cutting and thus stretching of the cuttingstrip is reduced. Also, due to the open space between the transverselyspaced cutting teeth and due to the continuous surface provided by theflat base 48, the cutting strip of the present invention provides asmooth outward flow of chips during the cutting operation.

Referring now to FIGURE 4, wherein like reference numerals refer to likeand corresponding parts previously described, the driving mechanism forthe cutting strip 22 is illustrated in greater detail. The drivesprocket wheel 24 rotates in a counterclockwise direction and includes aplurality of radially outwardly extending sprockets 70 for drivinglyengaging the driving surfaces 52 of the cutting teeth 44. In thepreferred embodiment the sprocket wheel 24 was constructed with a widthof about .375 inch and an outside diameter of about 2.14 inches,sprocket to sprocket.

Each sprocket 70 contacts a cutting tooth near the junction of thecutting tooth with the flat base portion 48 of the cutting strip 22, butthe sprockets 70 are so dimensioned to leave a small clearance betweenthe end of the sprocket and the flat base portion 48. As the sprocketwheel 24 is rotated, a sprocket 70 moves upwardly from the base of acutting tooth driving surface 52 to propel the cutting strip 22 forward.Just as the cutting tooth contacting sprocket clears the top of thecutting tooth, the next sprocket 70 contacts the base of the nextcutting tooth to provide a continuous drive of the cutting strip 22. Itshould be noted that although the preferred embodiment illustrates arotating drive Wheel disposed outside the periphery of the flexiblecutting strip 22, the drive wheel could be disposed inside the peripheryof the strip and drivingly contact the guide members.

The slope of the cutting teeth driving surfaces 52 causes the forcevectors provided by the sprockets 70 on the driving surfaces 52 to be sodirected as to push the cutting strip 22 against the outside peripheryof the support member 20 to provide a positive drive of the cuttingstrip. By varying the slope of the cutting teeth driving surfaces 52,the direction of the force vectors of the sprockets 70 may be changed,thus also changing the magnitude of the driving tension placed upon thecutting strip 22. Further, because the sprocket wheel 24 is disposedoutside the periphery of the rotating cutting strip 22, a continuousdrive is maintained against the cutting strip even upon the occurrenceof substantial cutting forces. The present driving mechanism for thecircular saw does not tend to bend or kink the cutting strip 22 when thecutting teeth become bound or locked into the material being cut. Theuniform drive provided by the driving sprocket wheel reduces wear andbending loads on the cutting strip to allow the use of thinner bandsteel. As previously discussed, the substantialiy circular andcontinuous travel path provided by the support member 20 reduces flexingof and thus provides a longer life for the cutting strip 22.

To further reduce frictional losses, lubricant may be supplied betweenthe support member 20 and the cutting strip 22. A constant flow oflubricant may be conventionally supplied to a chamber 72 (FIGURES 4 and7) and then through a passage 74 to a circumferential groove 76 disposedaround the support member 20. Due to the rotary motion of the cuttingstrip 22 and pressure supplied to the lubricant, a thin film oflubricant is disposed about the periphery of the support member 20 inorder to substantially reduce frictional losses of the saw. As shown 6in greater detail in FIGURE 7, the lubricant may be supplied by aconventional pump arrangement through channels 78 and 80 into thelubricant chamber 72.

Referring to FIGURES 4 and 5, the internal construction of the drivemechanism for the sprocket wheel 24 is illustrated. Portions of thedrive belt or chain 26 engage with teeth of a drive wheel 82 which isjournaled in the support extension 18 by suitable bearing members 83. Aguard housing 84 is connected to the extension 18 by suitable screws 86and is disposed over the wheel 82 for safety. The drive wheel 8-2 fitsthrough the sprocket wheel 24 and is connected to rotate the wheel 24 bya key member 88. A suitable fastening nut 90 is provided to suitablytension the sprocket wheel 24 on the rotating drive wheel 82. Aspreviously described, the guide members 46 encompass portions of theperiphery of the support member 20 to constrain the cutting strip 22 tofollow a circular travel path.

FIGURES 4 and 6 clearly illustrate the interlocking expansion joint 40,which is located below the contact point of the spocket wheel 24 withthe cutting strip 22 in order to prevent undue stress upon the expansionjoint. One end of the split circular support member 20 is firmlyconnected to the support extension 18 by a suitable fastening device 35.This fixed end of the circular support member 20 is provided with anextension 92 which defines a slot portion 93. The adjustable end of thesplit support member 20 includes a mating extension 94 which close- -lyfits into slot portion 93 and which defines a slot portion for matinglyreceiving extension 92. The ends of the extensions 92 and 94 arebeveled, and the slot portions 93 and 95 have beveled shoulders to matewith the extension ends when the joint is fully interlocked. Byselecting positioning of the screw 36 in the elongated slot 38, themagnitude of the outer periphery of the circular support member 20 maythus be adjusted in magnitude in order to select the desired tension forthe cutting strip 22, While maintaining a substantially continuouscircular travel path. A spring may be disposed in the slot 38 to providecontinuous tension to the adjustable end of the support member 20.

From the foregoing detailed description, it will be apparent that apower saw constructed in accordance with the present invention providessubstantial advantages over power saws heretofore developed. Forinstance, the relatively flexible continuous cutting strip of thepresent invention may be very economically manufactured and may thus bethrown away when dull without necessitating time consuming sharpening.Because of its low intertia, the present saw may be virtuallyinstantaneously stopped. The present cutting strip does not stretch evenwith substantial use and provides a smooth outward flow of chips duringthe cutting operation.

As is apparent from the cross-sectional illustration of the guide bar 20and cutting strip 22 presented in FIG- URE 5, and the overallarrangement of these components as shown in FIGURE 1, the guide bar orrigid means 20 is fully operable to follow the fiat base or supportmeans 48 of the strip 22, as the strip 22 moves into a kerf cut bycutting teeth 44.

As will also be apparent, in view of the foregoing discussion and theappended drawings, the various cutting teeth 44 are connected to thebase 48 by connecting sheet metal portions 44a. These connectingportions 44a, as i1- lustrated and described, are integral portions ofthe strip 22 and are supported immediately adjacent the guide bar 20 forsubstantially non-flexing movement through the circular travel pathdefined by the guide bar periphery.

Additionally, a power saw constructed in accordance with the presentinvention eliminates flexing of the continuous cutting strip and thusprovides a longer life of the saw because of low frictional losses andlow heat generation. The present saw is extremely easy to lubricate, andin fact requires less lubrication because of its novel method ofconstruction and operation. Because of the provision of the novelexpansion joint of the circular support member, tension on the cuttingstrip may be selectively adjusted while maintaining a continuous travelpath for the cutting strip.

It will be understood that while a preferred embodiment has beendescribed, the invention should not be limited to the exact method orapparatus illustrated, as various modifications which do not depart fromthe essence of the invention will be obvious to those skilled in theart.

What is claimed is:

1. A power driven saw comprising:

rigid means defining a substantially circular and continuous travelpath;

a radially flexible continuous cutting strip disposed in the travel pathfor rotation therethrough;

said cutting strip having a relatively fiat base with integral cuttingteeth being bent transversely of the base, and

said flat base and cutting teeth comprising integral portions formedfrom unitary sheet metal strip means;

said rigid means being disposed in supporting engagement with said fiatbase of said cutting strip and operable to follow said cutting stripinto a kerf cut by said cutting teeth; and

driving means for rotating said cutting strip through the travel path.

2. A portable saw comprising:

rigid means defining a substantially circular and continuous travelpath, said rigid means having external side portions spaced axially ofsaid travel path;

a generally circular, continuous cutting strip disposed in said travelpath for rotatable movement about said rigid means and for substantiallynonflexing rotation through said travel path;

said cutting strip including sheet metal, support means mounted on saidrigid means for rotation thereabout, extending transversely of saidrigid means, and disposed radially outwardly but adjacent to said rigidmeans;

a first plurality of sheet metal-defining cutting teeth extendingtransversely of said sheet metal support means and generally alignedalong one portion of said circular travel path,

a second plurality of sheet metal-defined cutting teeth extendingtransversely of said support means and generally aligned along anotherportion of said circular travel path and spaced radially from said firsttravel path portion,

sheet metal connecting portions between each tooth of said first andsecond plurality of sheet metal-defined cutting teeth and said supportmeans, said connecting portions being supported immediately adjacentsaid rigid means and mounted for substantially nonflexing movementthrough said circular travel path, and

sheet metal guide means extending transversely of said support means andslidably engaging said external side portions of said rigid means toconstrain said strip to travel through said travel p t said supportmeans, first plurality of cutting teeth, second plurality of cuttingteeth, guide means, and connecting portions comprising integral portionsformed from unitary sheet metal strip means;

said rigid means being disposed in supporting engagement with saidsupport means of said cutting strip and operable to follow said supportmeans into a kerf cut by said first and second plurality of cuttingteeth; and

driving means engaged with said cutting strip and operable to rotatesaid cutting strip about said rigid means.

3. A portable saw comprising:

rigid means defining a substantially circular travel path;

a generally circular, continuous cutting strip disposed in said travelpath for rotatable movement about said rigid means and for substantiallynonflexing rotation through said travel path;

said cutting strip including sheet metal, support means mounted on saidrigid means for rotation thereabout, extending transversely of saidrigid means, and disposed radially outwardly but adjacent to said rigidmeans,

a plurality of sheet metalxiefined, cutting teeth eX- tendingtransversely of said sheet metal support means and generally alignedalong said circular travel path,

sheet metal connecting portions between each tooth of said plurality ofsheet metal-defined cutting teeth and said support means, saidconnecting portions being supported immediately adjacent said rigidmeans and mounted for substantially nonflexing movement through saidcircular travel path; and

sheet metal guide means extending transversely of said support means,and slidably engaging said rigid means to constrain said strip to travelthrough said path,

said support means, plurality of cutting teeth, guide means, andconnecting portions comprising integral portions formed from unitarysheet metal strip means;

said rigid means being disposed in supporting engagement with saidsupport means of said cutting strip and operable to follow said supportmeans into a kerf cut by said plurality of cutting teeth; and

driving means engaged with said cutting strip and operable to rotatesaid cutting strip about said rigid means.

4. A power driven saw comprising:

means defining a substantially circular travel path;

a continuous cutting means disposed in said travel path forsubstantially nonfiexing rotation therethrough; said cutting meanshaving flexible base means with cutting teeth means mounted thereon,

said flexible base means and cutting teeth means comprising unitaryportions of sheet metal means;

said means defining a substantially circular travel path being disposedin supporting engagement with said flexible base means of said cuttingmeans and operable to follow said cutting means into a kerf by saidcutting teeth; and

driving means for rotating said cutting means through said travel path.

5. A power driven saw as described in claim 1 further comprising:

circumferentially overlapping portions of said rigid means disposed inaxially continguous relation; and

selectively operable means operable to induce relative circumferentialmovement between said overlapping portions and maintain said overlappingportions in axially continguous relation.

6. A power driven saw as described in claim 1 further comprising:

a first series of circumferentially spaced driving surfaces formed bysaid cutting teeth generally along one side of said cutting strip;

a second series of circumferentially spaced driving surfaces formed bysaid cutting teeth generally along another side of said cutting strip;and

rotary means included in said driving means and operable to drivinglyengage said first and second series of driving surfaces.

7. A power driven saw as described in claim 1 wherein said cutting teethcomprise:

a plurality of circumterentially spaced pairs of individual cuttingteeth;

the individual cutting teeth in each pair of cutting teeth beinggenerally axially displaced with respect to said travel path;

the axial distance between the individual cutting teeth of said pairs ofcutting teeth varying, on a repeated cyclic basis, circumferentiallyabout said cutting strip.

8. A power driven saw as described in claim 1 further comprising:

circumferentially overlapping portions of said rigid means disposed inaxially contiguous relation;

selectively operable means operable to induce relative circumferentialmovement between said overlapping portions and maintain said overlappingportions in axially contiguous relation;

a first series of circumferentially spaced driving surfaces formed bysaid cutting teeth generally along one side of said cutting strip;

a second series of circumferentially spaced driving surfaces formed bysaid cutting teeth generally along another side of said cutting strip;

rotary means included in said driving means and operable to drivinglyengage said first and second series of driving surface; and

a plurality of circumferentially spaced pairs of individual cuttingteeth included in said cutting teeth of said cutting strip;

the individual cutting teeth in each pair of cutting teeth beinggenerally axially displaced with respect to said travel path; and

the axial distance between the individual cutting teeth of said pairs ofcutting teeth varying on a repeated cyclic basis circumferentially aboutsaid cutting strip.

References Cited UNITED STATES PATENTS 2,351,738 6/1944 Blum l431352,804,105 8/1957 Stone 143-44 3,135,304 6/1964 Breer et a1. 143-443,338,275 8/1967 'Ehlen 143-32 FOREIGN PATENTS 396,208 1/ 1909 France.

DONALD R. SCHRAN, Primary Examiner U.S. Cl. X.R. l4332, 135

